Does driving at 55 use less gas then driving at say 65 or 70?

[klah]

Originally posted by: glugglug

The steep decay curve shown there is BS propaganda used by our gov't to try to justify the speed tax.

Looks like it depends on the car: http://www.startribune.com/stories/1608/5570755.html

Old Cutlass fuel economy decreases by 2% from 55-70 while an Olds Delta88 and Mercury Villager both decrease 24%.

 

[kranky]

I recently made a 250 mile highway trip (flat) and by experimenting a bit found out that for my car, a steady 64 mph gave me 37 mpg, in a huge Buick. An earlier trip where I varied speeds from 65-75 was 33 mpg.

I'm amazed I could get 37 mpg in that car at any speed.

 

[vegetation]

There's no way to tell unless you draw up data and make an analysis of it, while keeping other variables the same (i.e. same amount of gas in tank, one driver, same temps, etc). That wouldn't be so easy to do in a short time frame unless you have no life and are bored to death.

I believe the consensus would be that one should drive at a constant pace, as to not having to accelerate or deccelerate. Unfortunately for many urban areas, this is near impossible because of asshats driving far too slow and/or high traffic conditions.